Thread: 2hp extractor sounds like an air raid siren

One way to find out is to remove the 5" hose and fitting from the housing and see if there is any changes to the sound. Might shake the dust off the roof though.

Pete

It hasn’t got a foreign body trapped in the hoses or fan area has it?

Nope, it sounded like this from new. I'll try pulling the outlet hose off and see.

If it's a hissing noise that can be a good sign its moving lots of air but if its a howling/screeching noise that is a sign of something related to the impeller.

The maximum air compression point (narrowest part) of the air path in the impeller may have something a loose or a point/edge, or some other feature can sometimes cause this noise. Sometimes fixing a ~5 mm wide by 1-2 mm thick strip of wood or plastic across the full height of the outside of the inner wall of the impeller (see red area on picture) can help reduce noise. The piece can be held in place temporarily using double sided tape or very small REE. You may have to experiment with locations but somewhere near the air outlet is a place to start.

Sometimes The wood/plastic strip should be streamlined (ie bevel the edges). Sometimes an unbevelled piece works better?


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Thanks Bob, I'll look in to that. It's definitely not the sound of air moving, if I stand in the right place I can feel my whole chest resonating with it.

My Cleanspace2 respirator matches my breathing by monitoring air pressure and I actually noticed that the fan was pulsing quite quickly when my head was near the hose (it's just a 3m run of 6" flex with a bell-mouth for a lathe). The noise also seems to be coming down the hose to the open end, rather than being at the machine, maybe it's cavitating?

Did it only recently develop the noise?
If so it could also be that the impeller has gone out of balance or a motor bearing has gone.
The impeller out of balance could happen if something sticks to an impeller blade, or a piece of blade is knocked off or it picked up a hard piece of something and bent a blade OR . .

I'd be opening it up for a look.

It's always been like that; I doubt it's done more than 50 hours and it's all fine dust (metalwork lathe turning Tufnol, not woodwork), nothing that could possibly have damaged it. There's no physical vibration that I can feel on the housing.

I'll try the suggestions here and see. Hopefully it's an easy fix.

Originally Posted by elanjacobs

It's always been like that; I doubt it's done more than 50 hours and it's all fine dust (metalwork lathe turning Tufnol, not woodwork), nothing that could possibly have damaged it. There's no physical vibration that I can feel on the housing.

I'll try the suggestions here and see. Hopefully it's an easy fix.

Could have been a manufacturing flaw but if there's no vibe its unlikely to be a balance problem so I would go back to the initial post for ideas.

From the Clear Vue assembly instructions. They don't show an illustration with the location. Supports what Bob posted.

Do not remove the white block of wood mounted to the inside of your blower housing. This block counters the sound as the impeller blade passes by the larger opening of the blower housing, reducing noise.

I found a thread on it in the Clear Vue Forum. #8

Pete

Originally Posted by QC Inspector

From the Clear Vue assembly instructions. They don't show an illustration with the location. Supports what Bob posted.

Do not remove the white block of wood mounted to the inside of your blower housing. This block counters the sound as the impeller blade passes by the larger opening of the blower housing, reducing noise.

That's the sort of thing I was referring to in my first post in this thread

Just building on what you said Bob.

I do have a question though. Does that block have much of an effect on the airflow exiting the impeller housing?

Pete

We’d like to think the air flow through that narrow portion of the airflow path is nice and smooth but it’s far from that. The air flow at that point is highly turbulent and hence uneven so putting a “spoiler” of some kind can possibly just shift things around. I’d be looking for a foreign object or something out of alignment. If nothing the start off with something small eg 5x1 mm in cross section and experiment with location. A sound pressure level meter (mobile phone app) would assist in quantifying sound pressure levels.

Would small pieces, little squares positioned like vortex generators on an aircraft wing, or a series of bolt heads for example, be better than a bar across the width? Perhaps some thin super magnets could be placed in different spots until the best results were found before making something permanent. Not a good idea if the airflow will lift them off though.

Pete

Originally Posted by QC Inspector

Would small pieces, little squares positioned like vortex generators on an aircraft wing, or a series of bolt heads for example, be better than a bar across the width? Perhaps some thin super magnets could be placed in different spots until the best results were found before making something permanent. Not a good idea if the airflow will lift them off though.

Pete

Yep worth a go.